An InSb single crystal thin film grown by a conventional MBE method has large electron mobility and is suitable as a material of Hall elements or magneto-resistance elements. For example, it is reported that a 1.0 μm thick InSb thin film formed on a semiconductor GaAs substrate by doping a proper quantity of Sn has small temperature dependence of resistance and exhibits very high electron mobility, and hence it is a material capable of realizing highly sensitive magnetic sensors such as magneto-resistance elements or Hall elements operating in a wide temperature range (see Non-Patent Document 1). In addition, an InAs thin film is also a magnetic sensor material suitable for Hall elements and the like just as the InSb thin film (see Patent Document 1).
However, as for future magnetic sensor applications such as Hall elements, magnetic sensors are required to have higher sensitivity, lower power consumption and smaller temperature dependence, and thin film magnetic sensor materials are required to have higher electron mobility, higher sheet resistance and smaller temperature dependence. In addition, to meet such future magnetic sensor fabrication, thin film magnetic sensor materials are necessary, which have smaller temperature dependence of the resistance and electron mobility, and have higher electron mobility. Considering from such a point of view, it is essential to fabricate InSb thin films whose thickness is very thin and temperature dependence is small. However, when actually fabricating a InSb single crystal thin film on a GaAs substrate, for example, it is found that because of a large difference between their lattice constants, the electron mobility reduces drastically with the reduction in the film thickness in a range where the thickness of the InSb is less than 0.5 μm. As a result, fabrication of highly sensitive magnetic sensor is very difficult. Besides, there is another problem of marked characteristic deterioration in a practical magnetic sensor manufacturing process.
According to Non-Patent Document 1, it is generally known that when InSb is epitaxially grown on a GaAs substrate having a lattice mismatch, it has a three-layer structure that has layers with small electron mobility near its heteroepitaxial interface with the GaAs substrate and near its surface, and has the midsection with high electron mobility. It is considered that the low electron mobility layers are formed because of the lattice mismatch. As for the formation of the low electron mobility layer near the InSb surface, considering the surface of the InSb thin film as a heteroepitaxial interface with the vacuum (it can be considered a heteroepitaxial interface in a sense that it has not a party crystal lattice), it is understandable that it is formed because of the mismatch between the vacuum (atmosphere) and InSb.
Since a range (thickness) where the mismatch has an effect is considered to be nearly constant, the layers with small electron mobility near the heteroepitaxial interface with the GaAs substrate and near the surface have fixed thicknesses independently of the thickness of the InSb in its entirety, respectively.
Thus, the reduction in the electron mobility with the reduction in the thickness of the InSb occurs because of the reduction of the region (unaffected by the mismatch) with high electron mobility in the midsection involved in the reduction of the film thickness. Accordingly, it is expected that minimizing the regions affected by the mismatch can minimize the reduction in the electron mobility in spite of thinning the film. In other words, it is expected that eliminating the lattice mismatch of the heteroepitaxial interfaces formed on and under the operating layer can probably reduce or extinguish the thickness of the low electron mobility layers formed in adjacent to the heteroepitaxial interfaces.
FIG. 5 is a diagram showing relationships between the lattice constant (nm) and band gap energy (eV) of compound semiconductors for explaining the lattice mismatch in an InSb quantum well structure. As shown in FIG. 5, as for InSb, there is no insulating substrate material that makes lattice matching and has a large band gap. In addition, a narrow band gap material such as InSb has an essential, very important problem in that although it has large electron mobility, its resistance and electron mobility has great temperature dependence. Accordingly, when devices such as magnetic sensors are fabricated, they have large differences in resistance across driving terminals (referred to as “input resistance”) between a high temperature and a low temperature. Consequently, although it is comparatively easy to drive the elements around room temperature, as for recent applications which use them below −20° C. or up to a high temperature not less than 100° C., since the resistance value reduces with the temperature, the driving current increases with the temperature. Thus, it is necessary to protect the elements from damages due to over current, which imposes great restrictions on driving conditions, and presents a historically well-known problem in that the element driving becomes very difficult.
Furthermore, the large electron mobility will reduce the sheet resistance of the operating layer. When the film thickness of the operating layer is reduced to curb the reduction of the sheet resistance, the electron mobility reduces drastically because the low electron mobility layers are formed owing to the lattice mismatch in the substrate and surfaces as described above. Since the thicknesses of the low electron mobility layers do not change even if the film thickness of the operating layer is reduced, only the thickness of the high electron mobility layer reduces as a matter of course. Accordingly, the electron mobility reduces with the reduction of the film thickness, and the formation of the operating layer for fabricating the highly sensitive magnetic sensor becomes impossible.
In addition, according to experiments of the inventors of the present invention, it is well known that when the thickness of the operating layer is 0.5 μm or less in a single layer, and when an inorganic insulating protective film such as a protective film of SiO2 or Si3N4 is formed on the operating layer in the manufacturing process of fabricating the magnetic sensor, damage to the operating layer because of the protective film, which is referred to as process variation, can occur. In the case where the operating layer consists of InSb, although the damage is only about 10% when its thickness is 1.0 μm, the reduction of the electron mobility will reach 50% or more when it is 0.5 μm. Furthermore, the film thickness of 0.2 μm brings about the electron mobility reduction of 70% or more. It presents a more serious problem than the layer with the low electron mobility, which results from the exposure of the surface of the operating layer to a vacuum or air, and becomes a cause of hampering the fabrication of a practical highly sensitive magnetic sensor.
Such surface damage to the operating layer occurring at the protective film formation takes place because of collision of atoms or molecules, which come flying at the protective film formation and constitute the protective film, with the surface of the operating layer with kinetic energy as well as because of the lattice mismatch between the protective film and the operating layer or the difference in the crystal structure between the protective film and the operating layer, and presents a very serious problem yet to be solved. In addition, the damage reduces the reliability of the elements markedly, and increases variations of the characteristics of the elements fabricated. Furthermore, there is a very serious problem of being unable to use the thin film of the operating layer for fabricating practical highly sensitive magnetic sensors. It becomes a very difficult problem when trying to fabricate highly reliable practical magnetic sensors.
Conventionally, here is a reason why highly sensitive practical magnetic sensors cannot be fabricated by making effective use of the electron mobility in InSb-based thin films.
A thin film lamination has been required which has an operating layer suitable for highly sensitive magnetic sensor fabrication, which is able to produce, without the damage in the process, the magnetic sensors that are highly sensitive, have little temperature dependence, can be driven in a broad temperature range, and are superior in reliability such as high driving stability, that is, and that the operating layer of the magnetic sensors that have high sheet resistance, have high electron mobility, are free from the damage in the element manufacturing process, and have very small dependence of the sheet resistance or electron mobility on the temperature. However, the technologies up to now do not implement such thin film lamination.
In particular, it is very difficult to fabricate highly sensitive, low power consumption, very small temperature dependence thin film magnetic sensors such as Hall elements which have a narrow band gap thin film operating layer of 0.2 μm or less in thickness containing In and Sb, and they have not yet been realized.
In particular, when fabricating the Hall elements or magneto-resistance elements, the target is to reduce their power consumption and to increase their magnetic field detection sensitivity simultaneously, and further to zero the thickness of the low electron mobility layers, which are formed on the upper and lower sides of the operating layer of the magnetic sensor, or to keep the thickness very thin equivalent to zero, and simultaneously to minimize the temperature dependence of the operating layer including In and Sb.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a thin film lamination having an InAsSb-based operating layer, and a thin film magnetic sensor using the thin film lamination and a method for manufacturing the thin film lamination.
More specifically, the present invention aims to provide a thin film laminated material having a thin operating layer (thin film conducting layer) with high electron mobility, which is suitable for fabricating devices such as InAsSb-based magnetic sensors even if the operating layer is 1 μm or less in film thickness by extremely reducing the thickness of the low electron mobility layers caused by the effect of the lattice mismatch formed at the upper and lower sides of the operating layer. Furthermore, it aims, in such an element as described in Non-Patent Document 1, to provide a thin film with large electron mobility by securing a portion with high electron mobility in the midsection by extremely thinning or zeroing the low electron mobility layers of the operating layer, which exist near the interface making contact with the substrate and near the surface. Besides, it aims to fabricate a magnetic sensor employing as its operating layer a thin film with high electron mobility and high sheet resistance.
In addition, it aims to realize a guard structure of the operating layer that can prevent damage when forming the protective film in the fabrication process of the practical magnetic sensor, and to realize the operating layer with small temperature dependence.
Patent Document 1: Japanese Patent Laid-Open No. H6-77556 (1994).
Non-Patent Document 1: “Transport properties of Sn-doped InSb thin films on GaAs substrates” (Journal of Crystal Growth, Vol. 278 (2005), pp. 604-609)